In situ coordination-induced Langmuir film formation of water-soluble 2,5-dimercapto-1,3,4-thiadiazole at the air/water interface and the growth of metal sulfide nanostructures in their templated Langmuir-Schaefer films

Water-soluble bismuthiol(I) (2,5-dimercapto-1,3,4-thiadiazole, DMTD) was found to form stable Langmuir films on the aqueous subphase containing concentrated metal ions such as Cd(II), Cu(II), and Ag(I), although the compound had no long alkyl chain. It was confirmed that the Langmuir film formation was due to the in situ interfacial coordination between DMTD and the metal ions. The in situ coordinated Langmuir films could be transferred onto solid substrates by the horizontal lifting method as Langmuir-Schaefer (LS) films. The transferred LS films were characterized by a series of methods such as UV-visible spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy (AFM). The transferred LS films from the DMTD on metal ion subphases showed ordered layer structures with the layer distances of 0.68, 0.69, and 0.55 nm for the films transferred from the Cu(II), Cd(II), and Ag(I) subphases, respectively. The metal ion-coordinated DMTD ultrathin films could be used as templates to grow metal sulfides in aqueous Na2S solution. Pyramid morphologies of metal sulfides were obtained in the film. A possible growth mechanism was discussed. It was suggested that the alkyl-chain-free and water-soluble characteristics of DMTD play an important role in forming the large-sized, well-organized, and pyramid-shaped metal sulfide thin films.